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Oxygen Isotope Changes During Mica Alteration

Published online by Cambridge University Press:  02 April 2024

Sridhar Komarneni ,
Marion L. Jackson  and
David R. Cole
Sridhar Komarneni
Affiliation:
Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802
Marion L. Jackson
Affiliation:
Department of Soil Science, University of Wisconsin, Madison, Wisconsin 53706
David R. Cole
Affiliation:
Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
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Abstract

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Oxygen isotope analyses (δO18) of micas that were artificially depleted in K+ indicate little or no isotope exchange during the transformation. The oxidation of iron in K-depleted, iron-rich micas by H2O2 treatment resulted in 1.6 to 4.6% decrease in SO18 due to the fact that the equilibrium fractionation factor is less than the initial difference between the starting δO18 of the fluid and micas. The oxygen isotope ratio of a saponite formed by the weathering of phlogopite showed a 9.7% increase in δO18 due to authigenic recrystallization. These results suggest that oxygen isotope ratios can be used to determine the nature of chemical transformation during the weathering of mica to vermiculite and/or smectite.

Резюме

Резюме

Изотопный анализ кислорода (δO18) в образцах слюды, содержание K+ в которых было искуственно уменьшено, указывают на незначительный или нулевой изотопный обмен во время превращения. Результатом окисления железа в К-обедненных, обогащенных железом слюдах, при помощи обработки перекисью было уменьшение δO18 на 1,6 до 4,6‰ Это было вызвано тем, что величина равновесного коэффициента разделения была меньше, чем разница начальных значений δO18 для течи и слюд. Отношение изотопов кислорода для сапонита, образованного путем выветривания флогопита показало 9,7% увеличение значения δO18, вызванное аутогенной рекристаллизацией. Эти результаты указывают на то, что отношения изотопов кислорода могут быть использованы для определения природы химического превращения во время выветривания слюды и формирования вермикулита и/или смектита. [E.G.]

Resümee

Resümee

Sauerstoffisotopen-Analysen (δO18) von Glimmern, denen K+ künstlich entzogen wurde, zeigen geringen oder gar keinen Isotopenaustausch während der Umwandlung. Die Oxidation von Eisen in K+-verarmten, Eisen-reichen Glimmern durch H2O2-Behandlung führte zu einer Abnahme von 1,6 bis 4,6% bei δO18, aufgrund der Tatsache, daß der Gleichgewichtsfraktionierungsfaktor kleiner ist als der ursprüngliche Unterschied zwischen dem Ausgangswert δO18 der Flüssigkeit und dem der Glimmer. Das Sauer-stoffisotopenverhältnis eines Saponits, der durch Verwitterung von Phlogopit gebildet wurde, zeigte eine Zunahme von 9,7% des δO18-Wertes aufgrund autigener Rekristallisation. Diese Ergebnisse deuten darauf hin, daß die Sauerstoffisotopenverhältnisse dazu verwendet werden können, die Art der chemischen Umwandlung während der Verwitterung von Glimmer zu Vermiculit und/oder Smektit zu bestimmen. [U.W.]

Résumé

Résumé

Des analyses d'isotope oxygène (δO18) de micas dont on a artificiellement retiré K+ ont indiqué peu ou pas d’échange d'isotopes pendant la transformation. L'oxidation du fer dans des micas riches en fer, privés de K par traitement H2O a resulté en une diminution d’1,6 à 4,6% de δO18 à cause du fait que le facteur de fractionation d’équilibre est plus petit que la différence initiale entre le δO18 de départ du fluide et des micas. La proportion d'isotope oxygène d'une saponite formée par l'altération d'une phlogopite a montré une augmentation de 9,7% de δO18 à cause de la recristallisation authigénique. Ces résultats suggèrent que les proportions d'isotope oxygène peuvent être utilisées pour déterminer la nature de la transformation chimique pendant l'altération du mica en vermiculite et/ou en smectite. [D.J.]

Keywords

MicaOxygen isotopesPotassiumRecrystallizationSaponiteWeathering
Type
Research Article
Information
Clays and Clay Minerals , Volume 33 , Issue 3 , June 1985 , pp. 214 - 218
Copyright
Copyright © 1985, The Clay Minerals Society

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